java - 尝试为给定字段上的给定类创建比较器时出错

Question

我正在尝试创建一个在类的字段上重新返回比较器的函数，但是当我尝试获取 o2 的值时，在 Comparable v2 = (Comparable ) field.get(o2);，表示 lambda 参数无法转换为对象。有人可以帮忙吗？

public Comparator comp(String className, String fieldName) throws Exception {
    Comparator comparator = Comparator.comparing((o1, o2) -> {
        Class aClass = null;
        try {
            aClass = Class.forName(className);
            Field field = aClass.getDeclaredField(fieldName);
            field.setAccessible(true);
            Comparable v1 = (Comparable) field.get(o1);
            Comparable v2 = (Comparable) field.get(o2);
            return v1.compareTo(v2);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return 0;
    });
    return comparator;
}

Answer 1

您正在使用 Comparator.comparing 方法，但您传入的实际上是比较器的实现。您可以摆脱该方法调用并使用:

Comparator comparator = (o1, o2) -> {
    Class aClass = null;
    try {
        aClass = Class.forName(className);
        Field field = aClass.getDeclaredField(fieldName);
        field.setAccessible(true);
        Comparable v1 = (Comparable) field.get(o1);
        Comparable v2 = (Comparable) field.get(o2);
        return v1.compareTo(v2);
    } catch (Exception e) {
        e.printStackTrace();
    }
    return 0;
};
return comparator;

<小时/>

或者，您可以继续使用 Comparator.comparing 方法，但请记住，您应该传入提取字段值的函数:

public Comparator comp(String className, String fieldName) throws Exception {
    Class aClass = Class.forName(className);
    Field field = aClass.getDeclaredField(fieldName);
    field.setAccessible(true);
    Comparator comparator = Comparator.comparing(o1 -> {
        try {
            Comparable v1 = (Comparable) field.get(o1);
            return v1;
        } catch (Exception e) {
            throw new IllegalArgumentException(e);
        }
    });
    return comparator;
}